1. Field of the Invention
This invention relates to flying discs and particularly to toy discs thrown by hand in such a way as to have both forward and angular momentum.
2. The Prior Art
The type of toy with which this invention is concerned is similar to discs marketed under the trademark Frisbee by Wham-O Manufacturing Co. Such a toy has a relatively flat, circular central plate with an outer rim curved away from the plate to form a shallow dish. The edge of the rim has a rounded cross section resembling an air foil. The thickest part of the air foil is not immediately adjacent the edge but is perhaps one-third or so of the distance from the edge to the plate. The inwardly facing surface of the air foil section is substantially flat in cross section and, therefore, defines a generally cylindrical surface. The entire disc is molded of a suitable thermoplastic material, such as polyethylene, and the cylindrical configuration of the inwardly facing surface of the rim makes it easy to remove the disc from the mold.
While the central section has been referred to as a plate, it need not be perfectly flat, although it may be. Frequently this section is molded to have a slightly convex curvature as viewed from the side away from the rim. However, the central surface is so nearly planar that, for descriptive simplicity, it will be referred to as planar hereinafter.
Interest in the type of discs with which this invention is concerned is based on their flight characteristics. The shape of the disc gives it lift, when properly thrown, so that it does not simply sink to the ground as would a smooth, spherical ball of the same mass thrown with the same force. Some enthusiasts try to throw such a disc so that it flies as far as possible, and contests are held for that purpose. Other enthusiasts like to throw a flying disc of the shallow dish type back and forth to each other, either keeping the discs in the air or bouncing it off the ground somewhere between the players. Still other players try to cause their discs follow unusual, curved flight paths.
As might be expected, the various requirements of different players have led to different designs of Frisbee discs, the only brand of flying discs seriously considered by expert players. A main difference is in the weight, which may be as light as about 110 grams or as heavy as about 180 grams. Wind conditions have an important bearing on the particular discs that an enthusiast will select at a given time. Heavier ones are usually preferred in windy weather.
Although polyethylene does not shatter as would a more brittle material, it can be nicked, particularly when it is bounced off a paved surface or flies into an abrasive surface. The resulting projections from the originally smooth surface can make the disc painful to catch.
The flight characteristics of a flying disc are affected by the air foil and surface configuration, especially on the convex surface. Such discs are normally thrown with the rim extending downwardly from the plate, which is equivalent to saying that the convex surfaces face upwardly. For this reason the convex surfaces will be referred to as the upper ones and the concave surfaces as the lower ones in the following description.
There is a Right Hand Rule of Spinning Objects that is important in determining the flight path that will be followed by a spinning disc. It has been found desirable to mold slightly raised, concentrically circular ridges in the upper surface of a flying disc near the outer part thereof to reduce air drag and improve precessional qualities of the disc by counteracting the force produced by the Right Hand Rule just mentioned. U.S. Pat. No. 3,359,678 to Headrick describes such ridges, which interfere with air flow and therefore are called "spoilers". It is thought that such concentric ring spoilers have the greatest effect when the forward velocity of flying discs in scientific terms disc is greatest relative to the wind speed. Thus, the concentric ring spoilers are effective in flights for distance but are apparently not so much so in shorter flights.
Other publications that describe characteristics of Frisbees are the book FRISBEE by Stancil E. D. Johnson, M.D. published by Workman Publishing Company, New York, and a paper entitled "Adaptation of the Frisbee Flight Principle to Delivery of Special Ordinance" by G. D. Stilley of Honeywell Incorporated and D. L. Carstens of the Naval Ammunition Depot, Crane, Indiana, and presented at the AIAA 2nd Atmospheric Flight Mechanics Conference at Palo Alto, California, Sept. 11-13, 1972 (AIAA Paper No. 72-982).